Patent GB-485628-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/00
Filed: 1936-11-20
Abstract: 485,628. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., BOWSHER, E. A. H., and BRAY, F. H. Nov. 20, 1936, No. 31806. [Class 40 (iv)] Regenerative repeaters having registering and follow-up switches, for example, as described in Specifications 445,099 and 458,095, are associated with each end of a toll junction and are arranged to control also the transmission and reception of supervisory signals. All impulses and supervisory signals are transmitted over the junction by 50-cycle alternating current. Means is provided for preventing interference with the sending back of the signal denoting the called party's reply if the calling party sends further impulses by means of his dial or switch-hook. This feature forms the subject-matter of a divided Specification 485,635. In the system shown, the junction may be seized either by a toll operator or an automatic subscriber. The signals may be transmitted either over the physical junction circuit (with the crossed connections) or over a phantom circuit (with the dotted connections). Initiation of call. If the junction is seized by an operator, sleeve relay M energizes MM to mark the junction busy to the automatic selectors, and relay RR operates over the tip wire TW energizing DT which releases RR and completes a dialling loop to relay A. If seized by a subscriber, relay RR operates over the calling loop and energizes DT which extends the loop to relay A and connects battery to the sleeve wire SW to mark the junction busy to operators. In both cases, relays B, BT, BC, SD, ZC operate. Pick-up relay IG extends impulse springs MIS to magnet RM and relay CO so that switch R (rm1 .. rm3) moves two steps to position 3 and relay CO sends two 50-cycle impulses over the junction. Relay CG connects a resistance RCO across the line to prevent operation of receiving relay R by discharge currents. In position 3 of switch R, relay SC operates over wipers sm3, rm3 to stop impulsing. The impulses are received by relay IR, Fig. 3, and repeated by relay SA to magnet AM to advance switch A (am1 .. am4) to position 3 in which relay S operates closing a loop to the associated selector. Relay DI energizes in this loop and relay Y is operated by earth sent back from the selector and energizes AB, BX. Relay MC operates over wipers bm4, am4 and pick-up relay G extends springs IS to magnet BM and relay AO. Switch B (bm1 .. bm5) moves to position 3 and relay AO sends back two impulses which are repeated by relays R, RA to magnet SM to move switch S (sm1 .. sm3) to position 3. Relays RB, Z, ZA, DF, BB, BD, Fig. 2, and X, ZZ, XA, XB, Figs. 3 and 4, operate, relay DF connecting up dialling tone DTL, and relay BB releasing ZC so that ZB also operates. Dialling. Relay A repeats impulses to magnet RM through relay C which at the end of each digit charges a condenser over wiper rm1. Relay Z releases at the first step, followed by ZA, ZB and on the relapse of ZB, pick-up relay IG extends the springs MIS to magnet SM and to relay CO which transmits impulses over the junction. At each position of S at which a condenser is charged, an interdigital pause is inserted by the operation of relay Z, release of ZC, and the operation and release of ZA, ZB. The impulses are repeated at the incoming end to magnet AM where they similarly charge condensers over wiper am1 and regenerated impulses are transmitted at springs LIS in synchronism with the stepping of switch B, with inter-digital pauses determined by relays X, ZZ, XA, XB, XC. Relay PS operates during impulsing, disconnecting AD so that no signals can be sent in the reverse direction at this time. At the end of dialling, low resistance battery on the sleeve circuit energizes relay LR which releases DT and holds M and A. Reply signal. When the called party replies, relay D operates and energizes MD provided that X, XB and ZZ are operated, i.e. no impulses are coming in. Relay DDX operates to prevent any further incoming. impulses from stepping switch A, and relay MC releases to connect springs IS to magnet AM. Switch A moves two steps but relay AO sends only one (short) pulse since when A is one step in front of B, relay PS operates over wipers bm3, am4 to disconnect AO. When A is two steps ahead, relay MC operates to transfer the impulse circuit to magnet BM so that B also takes two steps and during this movement relay PC operates. Relay MC releases and switch A takes two further steps during which relay AO sends a single long pulse due to its locking circuit closed by PC. Relays PF, DFR operate, and the release of MC moves B two steps. The short pulse operates relays R, RA, ZB which disconnects the circuit to CO to prevent any signals being sent forward during the release period of ZB in case the calling party operates his dial or his switch-hook to prevent metering. During this period the long pulse arrives and effects the release of relay RB and the operation of DD to reverse the incoming connections to relay A. If such impulses are being sent before the arrival of the short pulse, relay CA, Fig. 3, operates CC to prevent the transmission of the long pulse until a time when a digital pause is being provided at the outgoing end. Release by called party. When the called party hangs up, relays D, MD, MC release and switches A and B move alternately two steps at a time in a manner similar to that already described. After each first step of A relay PS operates over wipers bm3, am4 to disconnect AO so that a series of spaced single pulses is sent back. Relays RA, SY, ZB operate, relay ZB remaining energized throughout the whole series of impulses to release DD which transmits a reversal back to the calling line. Called line busy. Busy flash signal sent back releases relay DI long enough to energize relay PR which energizes MD. Switch A sends back a preliminary short pulse as for a reply signal but in this case moves three steps owing to the connection of relay MC to wiper bm5. Relay B follows up three steps and during this movement relay PC operates. Switch A takes three further steps during which AO sends a long pulse followed by a short pulse. At the outgoing end, the long pulse releases relays RB, RD as before and the short pulse then operates BR to send back busy signals. Transferring calls. On receipt of a busy or called - party-clearing signal, the operator may set up a further call without taking down the plug. For this purpose, the cord-circuit ringing key is operated energizing relays RR, TR and releasing LR, DE, SY, A, B. Relay CO operates to send a signal over the junction as long as the ringing key is thrown. At the incoming end, relay SA remains energized long enough to release relay S so that the associated selector is released and the removal of ground from the third wire releases Y. During the release period of AB, a short acknowledgment pulse is sent back by AO and its receipt by RA releases the main holding relay BB. Release by calling party. The release of relays A, B, BT connects interrupted battery and earth on lead BB to relay CO which sends long pulses over the junction resulting in the release of relay S and the sending back of an acknowledgment signal to release BB as in the preceding paragraph. If the call is held by a distant manual operator, the removal of ground from the third wire to send back the acknowledgment and final release signal will be under the control of this operator. Re-ringing. A distant manual operator holding the connection as referred to in the preceding paragraph may re-ring a calling subscriber, operating relay RL (relay CA being operated periodically by the long pulses sent forward). Relay RL operates relay AT during a space between pulses and relay AO is connected to springs IS to send impulses back to the outgoing end. These operate RA, SY and release BC so that relay RG energizes and connects ringing-current to the calling line. Relay RT also operates. When the subscriber replies, the operation of relays A, B, BT, BC releases RG, RT and during the release period of RT relay CO sends a forward pulse which operates relay S to re-establish the direct-current loop.